The Class I MHC Protein and Tetramer Core will support research projects 1-3 and the TDC by providing Class I MHC proteins and tetramers carrying Category A-C agent peptides. While HLA-Class I-peptide tetramers are available commercially and through the NIH, production in a core facility will provide economies of scale, standardized production and quality assurance over time, and development of the expertise to extend production to additional alleles. The specific aims of the proposed Class I MHC Protein and Tetramer Core are: 1) to generate HLA Class I-peptide tetramers for use in detecting, quantifying, and characterizing Category A-C virus-specific CD8+ T cells; and 2) to generate purified HLA Class I-peptide complexes for use in the development of microassays to detect Category A-C virus-specific CD8+ T cells. The generation of HLA Class I-peptide tetramers or complexes will be prioritized based on identified epitopes and the distribution of HLA Class I alleles in the populations under study. The ready availability of HLA Class I-peptide tetramers to project investigators should greatly enhance their ability to enumerate, isolate, and characterize virus-specific CD8+ T cell responses in infected or vaccinated individuals.